IHG tends to have the biggest promotions if you follow their forum closely, followed by Marriott with Hilton in last place. One problem with Marriott promotions is that some of them require Visa. With Hilton you also get some additional points for booking and paying with American Express. Not sure what you have for a corporate card, so examine these issues. IHG does not seem to care what you pay with in terms of promotions though they do have a co-branded Visa card.